Gas detection devices are used, for example, in units for delivering and processing combustible and/or toxic gases in order to detect gases released in an unintended manner.
Gas detection devices that measure the concentration of harmful substances locally, i.e., in the immediate surrounding area, and are usually interlinked with one another in order to make it possible to monitor larger areas, are known.
There also are gas detection devices with an open measuring section, which are called open-path gas detection devices. The measuring section may range from a few m to a few hundred m. Open-path gas detection devices analyze electromagnetic or light radiation, which has passed through a defined monitoring range. The electromagnetic or light radiation is analyzed with respect to a possible interaction with a gas being released in an unintended manner, which is associated with a change in the properties of the radiation. This makes possible the continuous monitoring of a relatively large monitoring area with respect to an unintended release of gas, and the quantity and the species of the gas or gases being released can also be inferred from an analysis of the altered properties of the radiation. The radiation used for the monitoring may be, for example, thermal radiation of the background, or this radiation originates from a source of the gas detection device itself.
The functional devices used in gas detection devices have, as a rule, a limited field of view, i.e., these must be oriented relatively accurately towards the radiation source or the area to be monitored. This also applies to open-path gas detection devices, which comprise as functional devices, as a rule, at least one transmitter with a radiation source and a receiver with a radiation detector, to which the radiation emitted by the radiation source is focused. The radiation source may be, for example, a thermal radiator, for example, a xenon flash lamp, or a semiconductor radiator, for example, a tunable laser. Such open-path gas detection devices require orientation of both the transmitter and the radiation source integrated therein in order to direct a sufficient amount of radiation output to the inlet aperture of the receiver and the receiver in order for the radiation falling on the inlet aperture to reach the radiation detector as centrally as possible.
Another type of open-path gas detection device comprises a reflector, which is positioned at a distance of usually up to 50 m from a combined transmitter/receiver unit and onto which the radiation emitted by a radiation source is projected. The reflector reflects the radiation in the direction of the transmitter/receiver unit, as a result of which this can be detected by a radiation detector of the unit.
Another type of an open-path gas detection device is the so-called gas camera, whose spectral sensitivity is set to the absorption bands of a gas and which makes the gas being released from a leak visible or recognizes that gas by means of image processing and sends a warning signal.
Dräger Safety AG & Co. KGaA commercially offers an open-path gas detection device, in which both the transmitter and the receiver are connected with a baseplate by means of a joint arrangement each, which forms two pivot axes directed at right angles to one another. The joint arrangement is designed such that the two pivot axes intersect the optical axis of the radiation source and of the radiation receiver, respectively, approximately in the center of the housing of the respective functional device. Eight locking screws, four for the transmitter and four for the receiver, must be loosened and tightened after orientation to orient the transmitter or the receiver. The orientation itself is performed manually and can be checked by means of crosshairs, which is represented graphically on a hand-held device. A minimum signal is necessary for the analysis for displaying the crosshairs, so that a coarse orientation must be performed prior to the fine orientation by an optical direction finding, which can be carried out with the support of a telescope, which must be fastened to the housing of the transmitter or receiver in a defined manner. Once the orientation has been performed, the locking screws are tightened, so that the orientation is maintained unchanged for a rather long time period. Fine adjustment with strong holding force is advantageous for the accuracy of the orientation and for preserving the angle when tightening the locking screws.
Some open-path gas detection devices have adjusting screws with fine thread, which are used to orient the transmitter or the receiver with the locking screws loosened and transmit the translatory component of the screw motion to the transmitter or receiver in the process. As a consequence of the small pitch of the thread, accurate orientability of the transmitter and receiver can be achieved with these. If the adjusting screws are also used as locking screws at the same time, strong holding forces can, moreover, be brought about with these. This is especially advantageous when the adjusting/locking screws are arranged comparatively close to the respective axes of rotation. Adjusting or locking screws with fine thread are less suitable for use in an industrial environment because of the stresses due to contamination and corrosive media that are associated with them.